U.S. patent application number 10/646703 was filed with the patent office on 2004-03-04 for paste including a mixture of powders, connection plug, burying method, and semiconductor device manufacturing method.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Hayasaka, Nobuo, Hisatsune, Yoshimi, Kimura, Manabu, Sasaki, Keiichi.
Application Number | 20040043596 10/646703 |
Document ID | / |
Family ID | 26480926 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040043596 |
Kind Code |
A1 |
Sasaki, Keiichi ; et
al. |
March 4, 2004 |
Paste including a mixture of powders, connection plug, burying
method, and semiconductor device manufacturing method
Abstract
Form a trench in a major surface of a semiconductor substrate,
then bury a paste in the trench. The paste contains solids having a
conductive substance and a resin, and solvent for dissolving the
resin. The solids content of the paste is not less than 60 vol %
and a viscosity ratio thereof is not more than 2.
Inventors: |
Sasaki, Keiichi;
(Yokohama-shi, JP) ; Kimura, Manabu;
(Yokohama-shi, JP) ; Hisatsune, Yoshimi;
(Kawasaki-shi, JP) ; Hayasaka, Nobuo;
(Yokosuka-shi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Assignee: |
Kabushiki Kaisha Toshiba
Kawasaki-shi
JP
|
Family ID: |
26480926 |
Appl. No.: |
10/646703 |
Filed: |
August 25, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10646703 |
Aug 25, 2003 |
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09722467 |
Nov 28, 2000 |
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6657306 |
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09722467 |
Nov 28, 2000 |
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09321534 |
May 28, 1999 |
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6235624 |
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Current U.S.
Class: |
438/610 ;
257/E21.174; 257/E21.585; 257/E21.588; 257/E21.597; 257/E23.011;
438/612; 438/675 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 21/288 20130101; Y10S 438/977 20130101; H01L 21/76882
20130101; H01L 21/76877 20130101; H01L 2924/0002 20130101; H01L
21/76898 20130101; H01L 2924/00 20130101; H01L 23/481 20130101 |
Class at
Publication: |
438/610 ;
438/612; 438/675 |
International
Class: |
H01L 021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 1998 |
JP |
10-151800 |
Sep 11, 1998 |
JP |
10-258830 |
Claims
1. A paste containing: solids having a conductive substance and a
resin; and a solvent for dissolving the resin, wherein a solids
content of said paste is not less than 60 vol %.
2. A paste containing: solids having a conductive substance and a
resin; and a solvent for dissolving the resin, wherein a viscosity
ratio of said paste is not more than 2.
3. A paste containing: solids having a conductive substance and a
resin; and a solvent for dissolving the resin, wherein a solids
content of said paste is not less than 60 vol % and a viscosity
ratio thereof is not more than 2.
4. A connection plug buried in a connection hole of a substrate,
wherein said connection plug is made of a paste which contains
powder having different average particle sizes, and not less than
10% of said powder has an average particle size of not less than 3
.mu.m.
5. A method of burying said paste defined in claim 1 in a trench
formed in a major surface of a substrate.
6. A method of burying said paste defined in claim 2 in a trench
formed in a major surface of a substrate.
7. A method of burying said paste defined in claim 3 in a trench
formed in a major surface of a substrate.
8. A method of burying said paste defined in claim 4 in a trench
formed in a major surface of a substrate.
9. A method of burying powder in a trench formed in a major surface
of a substrate by coating a region including the trench with a
solution in which the powder disperses and precipitating the powder
in the solution.
10. A method according to claim 9, wherein a solution to which a
resin is added is used as the solution.
11. A method according to claim 9, wherein a portion of said powder
is a glass powder.
12. A method according to claim 10, wherein a portion of said
powder is a glass powder.
13. A method of manufacturing a semiconductor substrate, comprising
the steps of: forming a trench in a major surface of a substrate;
forming a calcination type paste inside and outside the trench, and
burying said paste in the trench; temporarily hardening said paste;
removing said paste outside the trench; and calcining said
paste.
14. A method according to claim 13, wherein said paste outside the
trench is removed by one of polishing and etching.
15. A method according to claim 13, wherein a connection plug made
of said paste extending through the substrate is formed by removing
an opposite surface of the substrate to the major until said paste
appears after the step of calcining said paste.
16. A method according to claim 13, wherein an interconnection is
formed on said paste after the step of calcining said paste.
17. A method according to claim 13, wherein a conductive paste is
used as said paste.
18. A method according to claim 13, wherein said paste outside the
trench is removed by chemical mechanical polishing.
19. A method according to claim 13, wherein a connection plug made
of said paste extending through the substrate is formed by removing
an opposite surface of the substrate to the major by one of
polishing and etching until said paste appears after the step of
calcining said paste.
20. A method according to claim 13, wherein a connection plug made
of said paste extending through the substrate is formed by removing
an opposite surface of the substrate to the major by chemical
mechanical polishing until said paste appears after the step of
calcining said paste.
21. A method of manufacturing a semiconductor device, comprising
the steps of: forming a trench in a major surface of a substrate;
burying a calcination type paste in the trench so as to leave a
space including at least a portion on a bottom surface of the
trench; filling a void in the trench with said paste by making a
pressure on said paste outside the trench higher than a pressure on
the void in the trench; and removing said paste outside the
trench.
22. A method according to claim 21, wherein the void in the trench
is filled with said paste by pressurizing said past outside the
trench.
23. A method according to claim 21, wherein after the step of
burying said calcination type paste in the trench under a reduced
pressure is performed to leave a space including at least a portion
of a bottom surface of the trench, the void in the trench is filled
with said paste by setting an atmospheric pressure higher than the
reduced pressure.
24. A method of manufacturing a semiconductor device, comprising
the steps of: forming a trench in a major surface of a substrate;
burying a calcination type paste in the trench so as to leave a
space including at least a portion of a bottom surface of the
trench; filling a void in the trench with said paste by making a
pressure on said paste outside the trench higher than a pressure on
the void in the trench; temporarily hardening said paste; removing
said paste outside the trench; and calcining said paste.
Description
BACKGROUND OF THE INVENTION
[0001] To improve the performance and, particularly, speed of an
electronic circuit system constituted by a plurality of
semiconductor chips, it has become increasingly important to reduce
the length of the interconnections between the semiconductor chips
to a minimum.
[0002] For this purpose, a technique of minimizing the
interconnections between a plurality of semiconductor chips by
stacking them has been studied instead of the conventional method
of mounting a plurality of semiconductor chips two-dimensionally on
a multilayer board. Such a semiconductor device formed by stacking
a plurality of semiconductor chips is called a multichip
module.
[0003] In addition, with the use of a multichip module of this
type, different types of semiconductor chips manufactured by
different processes can be stacked on each other into one hybrid
semiconductor device.
[0004] To manufacture a multichip module, vertically stacked
semiconductor chips must be electrically connected. For the
realization of such connection, the present inventors have already
proposed the use of connection plugs (chip-through plugs) that
extend through vertically stacked semiconductor chips to connect
them (Japanese Patent Application No. 9-305784).
BRIEF SUMMARY OF THE INVENTION
[0005] A paste according to the present invention is characterized
by containing solids having a conductive substance and a resin, and
a solvent for dissolving the resin, wherein a solids content is not
less than 60 vol %.
[0006] In the present invention, the solids content indicates the
ratio of solids (e.g., metals, glass, and resins) in a paste, which
are left on a substrate upon hardening the paste to the total paste
(solids+solvent). In the following description, this ratio
indicates the volume ratio unless otherwise specified.
[0007] In the present invention, the solids content of a paste is
set to 60 vol % or more for the following reason. When a paste is
hardened (dried) after it is buried in a trench with a squeegee,
the solvent in the paste volatilizes.
[0008] Upon this volatilization of the solvent, the volume of the
paste reduces. If the volume reduction of the paste is large, the
trench cannot be filled with the paste. A deterioration in buried
shape due to such a volume reduction can be effectively prevented
by increasing the solids content of the paste.
[0009] When the solids content is set to 60 vol % or more as in the
present invention, in particular, occurrence of a volume reduction
that causes connection failures and the like can be effectively
prevented, and the trench can be filled with the paste with a good
buried shape.
[0010] In addition, another paste according to the present
invention is characterized by containing solids having a conductive
substance and a resin, and a solvent for dissolving the resin,
wherein a viscosity ratio is not more than 2.
[0011] In the present invention, the viscosity ratio of a paste
indicates the ratio of viscosity changes in a case wherein the
viscosity of the paste is measured with a rotational viscometer at
rotational speeds that differ by one order of magnitude.
[0012] Assume that the viscosity of a given paste is measured with
the rotational viscometer at different rotational speeds, and
viscosities of 200 Pa.s and 100 Pa.s are respectively measured at
10 rpm and 100 rpm. In this case, the viscosity ratio is 200
Pa.s/100 Pa.s=2. The burying ratio of a viahole is the ratio of the
paste to the sectional area of the viahole when the cross-section
of the viahole is observed after a paste burial test.
[0013] In the present invention, the viscosity ratio of a paste is
set to 2 or less for the following reason. When the viscosity ratio
is high, the viscosity of the paste receiving force from the
squeegee becomes low. When the paste receives no force, the
viscosity increases. For this reason, when the paste is buried in a
trench with the squeegee, the viscosity of the paste becomes high
at the bottom portion of the trench. This makes it difficult to
bury the paste.
[0014] If, however, the viscosity ratio is set to 2 or less as in
the present invention, an increase in the viscosity of the paste at
the bottom portion of the trench can be effectively suppressed.
This prevents formation of voids that cause a connection failure
and an increase in resistance. Hence, the trench can be filled with
the paste.
[0015] Furthermore, still another paste according to the present
invention is characterized by containing solids having a conductive
substance and a resin, and a solvent for dissolving the resin,
wherein a solids content is not less than 60 vol % and a viscosity
ratio is not more than 2.
[0016] The trench can be filled with this paste with a good buried
shape.
[0017] In consideration of the buried shape, the viscosity of the
above paste is preferably 200 pas or less. In addition, if the
paste is to be used for a connection plug, the main component of
the paste should be a conductive substance.
[0018] A connection plug according to the present invention is a
connection plug made of a paste containing powder particles having
different average sizes and buried in a connection hole. This
connection plug is characterized in that the paste contains 10% or
more of a powder having an average particle size of 3 .mu.m or
more.
[0019] In this case, the paste preferably contains 10% or more of a
powder having an average particle size of 1 .mu.m or more. The
powder may be the main component of the paste or another component.
For example, the connection hole is a through hole extending
through a semiconductor chip.
[0020] The viscosity of the paste is determined by the total
surface area of powder particles in the resin contained in the
paste. As the total surface area increases, the viscosity
decreases. With the use of a connection plug containing a powder of
a large average particle size as in the present invention,
therefore, the paste as the connection plug can be buried in a
trench with a good buried shape. In addition, according to the
study conducted by the present inventors, it was found that the
occurrence rate of cracks could be reduced sufficiently by setting
the content of such a powder to 10% or more.
[0021] A burying method according to the present invention is
characterized in that a paste according to the present invention is
buried in a trench formed in the surface of a substrate.
[0022] With this arrangement, a good buried shape can be realized
even by a burying method using a squeegee.
[0023] In addition, the burying method according to the present
invention is characterized in that a powder dispersion is applied
on a region including a trench formed in the surface of a
substrate, and the powder is precipitated in the solution, thereby
filling the trench with the powder.
[0024] According to this arrangement, since the trench is filled
with the small-volume powder that precipitates, a deterioration in
buried shape, e.g., formation of a void, is suppressed.
[0025] In this case, as the above dispersion, a solution to which a
resin is added is preferably used. With the use of such a solution,
the powder particles can be temporarily fixed with the resin.
[0026] In addition, the powder preferably partially contains glass.
With the use of this powder, the glass melts in a calcination
process to fill the trench without any recess.
[0027] A method of manufacturing a semiconductor device according
to the present invention is characterized by comprising the steps
of forming a trench in a surface of a substrate, filling the trench
with a calcination type paste formed inside and outside the trench,
temporarily hardening the paste, removing an excess portion of the
paste outside the trench, and calcining the paste.
[0028] In the present invention, the excess portion of the paste is
removed in the step of temporarily hardening the paste, in which
the paste can be easily removed, instead of the step after
calcination in which the paste is difficult to remove. Even if,
therefore, the width of the trench increases, and the amount of
paste increases, an excess paste portion can be removed without
taking much time.
[0029] According to the present invention, therefore, even if the
width of the trench is increased to decrease the resistance of the
connection plug, an increase in the formation time of a connection
plug made of a paste can be suppressed.
[0030] Preferred aspects or more detailed forms of the
semiconductor device manufacturing method according to the present
invention will be described below.
[0031] (1) The excess portion of the paste outside the trench is
removed by polishing or etching. The above polishing is preferably
CMP (Chemical Mechanical Polishing). The above etching is RIE
(Reactive Ion Etching) or CDE (Chemical Dry Etching).
[0032] (2) After the paste is calcined, the lower surface of the
substrate is removed until the paste appears, thereby forming a
connection plug made of the paste penetrating the substrate. More
specifically, the lower surface is removed by polishing or etching.
The above polishing is preferably CMP. The above etching is RIE or
CDE.
[0033] In cases (1) and (2), after the trench is filled with the
paste to a certain degree, different pressures are applied to
portions inside and outside the trench, thereby filing an unfilled
region in the trench with the paste. Even if the depth of the
trench increases, the overall trench can be filled with the paste.
In these cases, therefore, even if the depth of the trench is
increased to decrease the resistance of a connection plug, a
connection plug made of a paste without any void can be formed.
[0034] (3) After the step of calcining the paste, an
interconnection is formed on the paste.
[0035] (4) This method is characterized by using a conductive paste
(plug body) as the above paste.
[0036] In cases (3) and (4), an insulating film is formed in
advance between the surface of the trench and the conductive paste.
If, however, an insulating substrate such as a ceramic substrate is
used as the above substrate, such an insulating film is not
required. Furthermore, if an insulating paste is used as the above
paste, a conductive film (connection plug body) is formed in
advance on the surface of the trench.
[0037] In addition, another semiconductor device manufacturing
method according to the present invention is characterized by
comprising the steps of forming a trench in a major surface of a
substrate, burying a calcination type paste in the trench so as to
fill a space including at least a portion on a bottom surface of
the trench, filling an unfilled region in the trench with the paste
by making a pressure on the paste outside the trench higher than a
pressure on the unfilled region in the trench filled with the
paste, and removing an excess portion of the paste outside the
trench.
[0038] Furthermore, still another semiconductor device
manufacturing method according to the present invention is
characterized by comprising the steps forming a trench in a major
surface of a substrate, burying a calcination type paste in the
trench so as to leave a space including at least a portion of a
bottom surface of the trench, filling an unfilled region in the
trench with the paste by making a pressure on the paste outside the
trench higher than a pressure on the unfilled region in the trench
filled with the paste, temporarily hardening the paste, removing an
excess portion of the paste outside the trench, and calcining the
paste.
[0039] According to the present invention, even if the width and
depth of a trench are increased to sufficiently decrease the
resistance of a connection plug, an increase in the formation time
of a connection plug made of a paste can be suppressed, and a
connection plug made of a paste without any void can be formed.
[0040] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0041] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0042] FIG. 1 is a graph showing the relationship between the
viscosity ratio of a paste and the burying ratio of a viahole;
[0043] FIG. 2 is a graph showing the relationship between the
solids content of a paste and the burying ratio;
[0044] FIG. 3 is a graph showing the relationship between the
average particle size of large powder particles, the occurrence
rate of cracks in the paste, and the content of large powder
particles;
[0045] FIGS. 4A to 4F are sectional views showing the steps in a
method of forming a chip-through plug according to the second
embodiment of the present invention;
[0046] FIGS. 5A and 5B are sectional views for explaining problems
posed in a conventional method of burying a paste in a trench
(screen printing);
[0047] FIGS. 6A to 6E are sectional views showing the steps in a
method of forming a connection plug according to the fifth
embodiment of the present invention;
[0048] FIGS. 7A to 7G are sectional views showing the steps in a
method of forming a connection plug according to the sixth
embodiment of the present invention; and
[0049] FIGS. 8A to 8D are sectional views showing the steps in a
method of forming a connection plug according to the seventh
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Embodiments of the present invention will be described below
with reference to the accompanying drawings.
[0051] The present inventors examined the conventional method of
forming a chip-through plug (Japanese Patent Application No.
9-305784) and found the following problem.
[0052] When the above chip-through plug is to be formed, a
conductive paste as a chip-through plug is buried in a trench
(opening diameter: 50 to 100 .mu.m; depth: 100 to 150 .mu.m) formed
in the surface of an Si substrate. The lower surface of the Si
substrate is then polished until the paste appears.
[0053] As a method of burying the paste, a burying method (screen
printing) using a squeegee is used because of its simplicity and
easiness.
[0054] In the method using the squeegee, however, the trench formed
in the surface of a substrate 81 cannot be sufficiently filled with
a paste 82. As a result, a recess 83 or a void 84 is formed.
[0055] Such a deterioration in the buried shape of the paste 82
causes a connection failure or an increase in resistance. This
problem become noticeable not only when the width of the trench is
increased to sufficiently decrease the resistance of the
chip-through plug but also when the depth of the trench is
increased.
[0056] Embodiments of the present invention which can prevent the
above deterioration in buried shape will be described below.
[0057] (First Embodiment)
[0058] In this embodiment, a paste is buried in a trench formed in
the surface of a substrate by a printing method using a squeegee.
In the conventional method, as shown in FIGS. 5A and 5B, voids and
recesses were formed in trenches because a paste is not
sufficiently buried in the trenches.
[0059] The present inventors found that the causes of this problem
were a change in the viscosity of the paste when buried with the
squeegee and the shrinkage of the paste upon volatilization (to be
referred to as hardening hereinafter) of the solvent of the paste.
To improve the buried shape of a paste, this embodiment therefore
uses a paste for which a viscosity change upon burial and a solids
content are controlled.
[0060] FIG. 1 shows the relationship between the viscosity ratio of
a paste and the burying ratio of a viahole. In this case, the
viahole has a depth of 50 to 200 .mu.m and an opening diameter of
100 .mu.m. The paste was buried under the condition that the
viscosity measured by a rotational viscometer became 150 Pa.s when
the rotational speed was 200 rpm. The average diameter of the paste
was set to 1 .mu.m. The viscosity ratio was controlled with the
resin component of the paste, and the solids content was set to 60
vol %.
[0061] As shown in FIG. 1, when the viscosity ratio is 3, the
viahole having an aspect ratio of 0.5 (depth of 50 .mu.m) exhibits
a burying ratio of 90%, but the viahole having an aspect ratio of 2
(depth of 200 .mu.m) exhibits a burying ratio of 40%.
[0062] It was found that viscosity ratios of 3 or less, 2 or less,
and 1.5 or less needed to be respectively set for the viaholes
having aspect ratios of 0.5 (depth of 50 .mu.m), 1 (depth of 50
.mu.m), and 2 (depth of 200 .mu.m) to ensure a burying ratio of 90%
or more.
[0063] Although the relationship between the burying ratio and the
viscosity ratio was obtained with the opening ratio ranging from 40
to 200 .mu.m and the depth ranging from 20 to 400 .mu.m, it was
found from the research conducted by the present inventors that
when the viscosity ratio was constant, the burying ratio was
determined by only the aspect ratio regardless of the depth.
[0064] The mechanism of increasing the burying ratio by keeping the
viscosity ratio constant can be explained by the load imposed by
the squeegee in burying the paste. When the viscosity ratio of the
paste is high, the viscosity of the paste decreases in the presence
of a force from the squeegee, but increases in the absence of a
force. For this reason, the viscosity becomes high at a bottom
portion of a trench at which the load from the squeegee is light,
hindering the paste from being buried.
[0065] As is obvious from the above description, the burying ratio
can be effectively increased by decreasing the viscosity ratio, and
a burying ratio of 90% or more can be obtained even at an aspect
ratio of 1 by setting the viscosity ratio to 2 or less.
[0066] FIG. 2 shows the relationship between the solids content of
the paste and the burying ratio. In this case, the paste was buried
in a trench by directly scanning the squeegee on the substrate
without using any mask. The viscosity ratio of the paste was 1.5.
The paste was buried under the condition that the viscosity
measured by the rotational viscometer became 150 Pa.s when the
rotational speed was 20 rpm.
[0067] As shown in FIG. 2, as the solids content increases, the
burying ratio increases. When the aspect ratio is 1, a burying
ratio of 90% or more can be obtained with a solids content of 60
vol % or more, and a burying ratio of 95% or more can be obtained
with a solids content of 70 vol % or more.
[0068] As is obvious from FIG. 2, when the aspect ratio is 0.5 or
more, a burying ratio of 90% or more can be obtained with a solids
content of 65% or more, and a burying ratio of 100% or more can be
obtained with a solids content of 80% or more.
[0069] The relationship between the solids content of the paste and
the burying ratio can be explained as follows. When the paste is
hardened after it is buried in a trench with the squeegee, the
solvent in the paste volatilizes. As a result, the volume of the
paste reduces by the amount of volatilized solvent. If this volume
reduction is large, the trench cannot be filled with the paste,
resulting in a great decrease in burying ratio.
[0070] As is obvious from the above description, the burying ratio
can be effectively increased by increasing the solids content, and
a burying ratio of 90% or more can be obtained even at an aspect
ratio of 1 by setting the solids content to 60 vol % or more.
[0071] As described above, the burying ratio can be effectively
increased by decreasing the viscosity ratio (preferably to 2 or
less) or increasing the solids content (preferably to 60 vol % or
more). More preferably, the viscosity ratio is decreased and the
solids content is increased at the same time.
[0072] In this embodiment, the viscosity of the paste was 150 Pa.s.
However, a high burying ratio could be realized between 100 to 200
Pa.s as in the embodiment.
[0073] To increase the solids content of the paste without
increasing-the viscosity of the paste to a high value, i.e., a
value exceeding 200 Pa.s, the density of the solids may be
decreased. For example, the amount of resin in the paste may be
increased, the glass component may be increased in amount, or a
low-density light metal may be used as a metal material.
[0074] Alternatively, the average particle size of the powder in
the paste may be increased. As the average particle size of the
powder increases, the surface area of the powder per unit volume
increases. As the surface area per unit volume increases, the
viscosity increases under the influence of the surface tension.
This increases the solids content while maintaining the viscosity.
Note that the powder may be the main component of the paste or
another component.
[0075] Although different values were obtained-in the paste
viscosity range of 50 to 400 Pa.s, similar tendencies were found in
this range. When, for example, the viscosity of the paste was 200
to 400 Pa.s, and the solids content was 60 vol %, the viscosity
ratio needed to be 1.5 or less to realize a burying ratio of 90% in
a trench having an aspect ratio of 1. This viscosity ratio was
lower than that in the embodiment (viscosity of 150 Pa.s).
Furthermore, a burying ratio of 90% or more could be realized at a
viscosity ratio of 3 or less.
[0076] In addition, a high burying ratio can be realized even by
using a metal, a glass material, a mixture, or a composite material
as a paste material.
[0077] In this case, to decrease the viscosity of the paste, the
particle size of the paste is preferably increased or the particle
size distribution of the paste is preferably made broad. The
particle size distribution of the paste may be made broad by using
a method of mixing powder particles with different average sizes.
When the particle size distribution is made broad, the viscosity
decreases to improve the buried shape and suppress occurrence of
cracks upon hardening.
[0078] When, for example, powder particles having average sizes of
1 .mu.m and 5 .mu.m are mixed in an Ni paste, the occurrence rate
of cracks in the paste-becomes 1/2 or less that in an Ni paste
obtained by mixing only a powder having an average particle size of
1 .mu.m. Note that the powder may be made of Ni or another
material.
[0079] FIG. 3 shows the relationship between the average size of
large powder particles, the occurrence rate of cracks in the paste,
and the content of large powder particles (large powder
particles/all powder particles [wt %]) when powder particles
containing large powder particles having a size of 1 .mu.m or more
are mixed in the paste. In this case, the average particle size of
the paste is 1 .mu.m, and the average sizes of the large powder
particles are 1 .mu.m, 2 .mu.m, and 3 .mu.m, respectively.
[0080] As is obvious from FIG. 3, when the large powder particles
having an average size of 3 .mu.m are used, the occurrence rate of
cracks in the paste can be suppressed to 80% by setting the content
of the large powder particles to 10% or more, and the occurrence
rate of cracks can be suppressed to about 20% or less by setting
the content to 60% or more.
[0081] In practicing the present invention, in consideration of its
mechanism, the resin and solvent in the paste need not be
specified. Even if, for example, ethyl cellulose, terpineol, or
acrylic resin is used as a resin, the paste can be buried in the
same manner as in this embodiment as long as the above conditions
for viscosity ratios and solids contents are satisfied.
[0082] When a metal paste is used, the amount of resin is
preferably small in consideration of a decrease in resistance. When
a paste was to be finally formed in only a trench, in particular,
only a minimum amount of resin was required for temporary holding,
and 3% or more of the total paste was sufficient for the amount of
resin for temporary holding.
[0083] In addition, if the amount of resin is 6 wt % or more, since
the solvent and solids in the paste do not separate from each
other, long-term storage is facilitated. If, therefore, a paste is
to be simply formed, the amount of resin is preferably 6 wt % or
more.
[0084] If the wettability between a paste and a substrate was poor
in a burying process, the buried shape deteriorated. When the
viscosity of the paste was 50 Pa.s or less, in particular, the
buried shape was improved by improving the wettability between the
paste and the substrate. For example, the wettability can be
improved by performing ultrasonic cleaning of the substrate with
the solvent in the paste, cleaning the substrate with a surfactant,
or using a surfactant-containing paste.
[0085] (Second Embodiment)
[0086] In this embodiment, a chip-through plug (connection plug)
for a multichip module is formed by using a paste having excellent
burying characteristics as in the first embodiment.
[0087] The following conditions are required for a chip-through
plug. The chip-through plug must be sufficiently buried in a trench
to allow the chip to make lower-surface contact. The upper portion
of the chip-through plug (to be referred to as the plug upper
portion hereinafter) must be flat to allow an interconnection to be
formed on the plug upper portion. The lower portion of the
chip-through plug (to be referred to as the plug lower portion
hereafter) must have wettability with respect to a repairable
material such as a solder and be dense not to absorb a solder or
the like.
[0088] As a method of satisfying such requirements, a method of
improving the buried shape, planarization, and denseness of a
chip-through plug by forming sputtered films on both the plug upper
portion and the plug lower portion is available. In this
embodiment, however, a method of improving these properties by a
paste itself. According to this method, a chip-through plug can be
formed by using only a paste. Since the step of forming sputtered
films is not required, the process is simplified.
[0089] FIGS. 4A to 4F are sectional views showing the steps in a
method of forming a chip-through plug according to this embodiment.
First of all, as shown in FIG. 4A, a trench is formed in the upper
surface of an Si substrate 1, and a paste containing materials such
as Ni, Cu, and Au exhibiting good wettability with respect to a
solder and having a small particle size distribution (to be
referred to as a fine paste hereinafter) 2 is deposited on the
entire surface of the trench to cover the bottom and side surfaces
of the trench. At this time, the trench is not filled with the fine
paste 2.
[0090] As shown in FIG. 4B, the trench is filled with a paste
having a large particle size distribution and exhibiting a high
burying ratio (to be referred to as a buried paste hereinafter) 3
like the one described in the first embodiment by a burying method
using a squeegee.
[0091] As shown in FIG. 4C, that excess portion of the buried paste
3 outside the trench and the buried paste 3 slightly below the
opening surface of the trench are removed by polishing or etching.
As a result, an unfilled portion is formed in the upper portion of
the trench. Thereafter, the fine paste 2 and the buried paste 3 are
calcined.
[0092] As shown in FIG. 4D, a fine paste 4 is deposited on the
entire surface of the resultant structure to fill the unfilled
portion.
[0093] As shown in FIG. 4E, the excess portion of the fine paste 4
outside the trench is removed by CMP to planarize the upper
surface, and the fine paste 4 is calcined. Note that the fine paste
2 and the buried paste 3 may not be calcined in the step in FIG.
4C, but all the paste 2 to paste 4 may be calcined altogether in
the step in FIG. 4E.
[0094] Finally, as shown in FIG. 4F, the lower surface of the Si
substrate 1 is polished to expose the fine paste 4, thus completing
the chip having the chip-through plug made up of the fine paste 2,
the buried paste 3, and the fine paste 4 and extending through the
Si substrate 1.
[0095] Note that the use of an appropriate slurry in the step in
FIG. 4C will obviate the necessity of the fine paste 4 for
planarizing the plug upper portion. More specifically, this step
may use a slurry that can remove the main component of a paste (for
example, Ni if an Ni paste is used) by CMP in which the
contribution of chemical polishing is larger than that of
mechanical polishing.
[0096] The use of such a slurry can prevent the paste 3 and paste 4
from being physically polished to an excessively low level by
mechanical polishing even if the upper portions of the paste 3 and
paste 4 contain large particles of the main components. Therefore,
the upper surface can be planarized.
[0097] (Third Embodiment)
[0098] As a method of burying a filling member having conductivity
such as a chip-through plug in a trench, a method of dispersing a
conductive powder with a solvent in advance, applying this powder
(powder+solvent) on the substrate in which the trench is formed,
and precipitating the powder in the solvent, thereby burying the
powder in the trench is available in addition to the method of
burying a paste with a squeegee.
[0099] For example, an Ni powder having an average particle size of
1 .mu.m is dispersed in a methanol solution, and the solution is
applied to a substrate in which a plug is formed. Since the
dispersed NI powder precipitates, the Ni powder is deposited on the
substrate. The substrate is then dried to evaporate the methanol.
Thereafter, the Ni powder is calcined. As a consequence, the powder
is completely buried in the trench (this method will be referred to
as the precipitation method hereinafter). After this process, the
Ni powder portion calcined outside the trench is removed, as
needed.
[0100] In burying the powder in the trench by the precipitation
method, since the binding force between the particles of the powder
in the trench is lost upon volatilization of the solvent, a resin
is preferably dissolved in the solvent to allow the powder
particles to precipitate and combine with each other upon
precipitation of the powder or volatilization of the solvent.
[0101] As methods of fixing the powder, a method of sealing the
powder with a resin upon volatilization of the solvent and a method
of forming a film on the opening surface of the trench are
available. In the latter method, since no resin is contained in the
powder, the powder can be calcined without being influenced by the
atmosphere in calcination.
[0102] Although the method of fixing the powder has been described
above, if no vibration is applied to the stage, the powder need not
be fixed.
[0103] In addition, a chip-through plug for the multichip module of
the second embodiment can also be formed by using the precipitation
method of this embodiment.
[0104] More specifically, a powder of a small particle size (fine
powder) is precipitated first, and then a powder of a large
particle size (buried powder) is precipitated. The buried powder
outside the trench and the buried powder and fine powder slightly
below the opening surface of the trench are removed. Finally, a
fine powder precipitates on an unfilled portion of the trench.
These powder portions may be calcined collectively or
separately.
[0105] Alternatively, the precipitation method may be performed by
using a powder obtained by mixing large powder particles and small
powder particles. In this case, the stepped portion on the upper
portion can be improved by performing control such that the large
powder particles precipitate first, and the small powder particles
are deposited thereon.
[0106] In the precipitation method described above, wettability
between the substrate and the solvent used for the method is
important. If a solvent of poor wettability must be used as a
dispersant for the powder, a method of physically improving the
quality of the powder by using ultrasonic waves or a method of
improving the quality of the solvent by using a surfactant must be
used together. When, however, the viscosity was about 20 to 50
Pa.s, i.e., the viscosity was relatively high, wettability did not
have much influence.
[0107] In addition, to shorten the precipitation time of the
powder, a coagulant that weakens the effect of the dispersant may
be added or precipitation may be speeded up by using centrifugal
force.
[0108] (Fourth Embodiment)
[0109] In the burying method of a paste using a squeegee (screen
printing), the particle size of the paste, particle size
distribution, and particle shape influence paste burial.
[0110] The particles of a paste used for a chip-through plug are
preferably fine particles in order to planarize the plug upper
portion.
[0111] When a paste is to be buried by screen printing, the average
size of the particles of the paste is preferably 0.5 .mu.m or more
and 5 .mu.m or less. In addition, particles having an average size
of 1 .mu.m or less are preferably 10% or more, and particles having
an average size of 3 .mu.m or more are preferably 10% or more.
[0112] When particles having an average size of 1 .mu.m are to be
exposed on the plug upper portion, the above particles must be
removed by CMP. The particles serve as the main component of the
paste and other components.
[0113] As a particle shape, a shape with a large particle area,
e.g., a confetto-like shape, is effective in increasing the
viscosity. In addition, owing to many projections of this shape,
conduction improves in calcination, resulting in a decrease in
resistance.
[0114] The particle size distribution in screen printing is
important. If large particles are required to control the particle
size distribution, the use of a glass material as such material,
which dissolves in calcination, can improve the buried shape and
planarization.
[0115] If the main component of a paste is Au, it is difficult to
increase the solids content by using only Au because of high
density. For this reason, coating particles containing Ni as a
nucleus with Au can improve the buried shape while taking advantage
of the characteristics of the high-density material. In addition,
if no specific problem arises in a burying process, the buried
shape can be improved by intentionally adding a low-density
material.
[0116] The present inventors examined the conventional chip-through
plug forming method (Japanese Patent Application No. 9-305784) and
further found the following problems.
[0117] As a method of burying the above conductive paste, a burying
method using a squeegee (screen printing) is used because of its
simplicity and easiness.
[0118] In the burying method using a mask and a squeegee, a
conductive paste portion remains on an Si substrate by the amount
corresponding to the thickness of the mask, although it depends on
the method to be used.
[0119] In a case of a connection plug connected to a power supply
line, in particular, as the width of a trench increases because of
requirements for a decrease in the resistance of the connection
plug, a thicker conductive paste must be applied on an Si
substrate. As a consequence, a thicker paste portion remains on the
substrate.
[0120] In the method of burying a conductive paste by directly
applying it on an Si substrate with a squeegee without using any
mask, an excess conductive paste portion protruding from the
squeegee remains on the Si substrate.
[0121] When the excess conductive paste portion is removed after
the conductive paste is calcined, the thickness of the excess
conductive paste portion becomes as large as several tens .mu.m in
either of the above methods.
[0122] It takes much time to remove such a thick excess conductive
paste portion by CMP, resulting in an increase in the time required
to form a connection plug. This decreases the productivity of
multichip modules.
[0123] To further decrease the resistance of a connection plug,
both the width and depth of a trench are increased. In the burying
method using the squeegee, as a trench becomes thicker (aspect
ratio increases), the trench cannot be sufficiently filled with a
paste. As a result, a chip-through plug having a void is
formed.
[0124] An embodiment of the present invention which can solve the
above problems that arise when the size (width and depth) of a
trench is increased will be described below.
[0125] (Fifth Embodiment)
[0126] FIGS. 6A to 6E are sectional views showing the steps in a
method of forming a chip-through plug according to the fifth
embodiment of the present invention. In this embodiment, a
chip-through plug is formed in a ceramic substrate.
[0127] First of all, as shown in FIG. 6A, a trench 12 having, for
example, an opening diameter of 100 .mu.m and a depth of 200 .mu.m
is formed in the surface of a ceramic substrate 11 having, for
example, a width of 4 cm and a thickness of 0.8 mm. Thereafter, the
ceramic substrate 11 is calcined.
[0128] As shown in FIG. 6B, a calcined conductive paste 13 having a
thickness larger than the depth of the trench 12 is buried in the
trench 12 by the burying method (screen printing) using the
squeegee and a metal mask having an opening portion equal to or
larger than the opening diameter of the trench 12, e.g., a metal
mask having an opening diameter of 120 .mu.m and a thickness of 30
.mu.m. At this time, the excess portion of the conductive paste 13
which protrudes from the squeegee remains on the substrate (on the
trench 12 and its peripheral portion). The conductive paste 13
having a thickness smaller than the depth of the trench 12 may be
buried in the trench 12 as long as the trench 12 can be entirely
filled with the paste finally.
[0129] After the conductive paste 13 is temporarily hardened by a
heat treatment at 140.degree. C. for 10 min, the excess portion of
the conductive paste 13 outside the trench 12 is removed by CMP or
mechanical polishing (MP) using a grindstone, as shown in FIG.
6C.
[0130] At this time, since the conductive paste 13 is only
temporarily hardened, the excess portion of the conductive paste 13
outside the trench 12 can be removed by polishing with a weak force
enough to destroy the resin in the conductive paste 13.
[0131] As a result, the excess portion of the conductive paste 13
can be removed at a rate as high as 20 to 100 .mu.m/min as compared
with a low rate of 1 .mu.m/min in the conventional method. In this
embodiment, therefore, the excess portion of the conductive paste
13 can be removed in a very short period of time as compared with
the prior art.
[0132] The conductive paste 13 is then calcined at 500.degree. C.
to remove the resin component in the conductive paste 13 and ensure
conductivity of the conductive paste 13. The conductive paste 13 in
this step will be referred to as the chip-through plug 13
hereinafter.
[0133] Finally, as shown in FIG. 7D, the lower surface of the
ceramic substrate 11 is polished until the chip-through plug 13
appears, thereby completing the chip-through plug 13 extending
through the ceramic substrate 11. The above polishing is, for
example, CMP or MP. In addition, the lower surface may be removed
by etching such as RIE or CDE instead of polishing.
[0134] The subsequent steps are the same as those for a general
multichip module. For example, as shown in FIG. 6E, the subsequent
steps are the step of forming an interconnection 14 connected to
the chip-through plug 13 on the ceramic substrate 11 and the step
of forming an interlevel insulating film 15 on the entire surface
of the resultant structure and forming a connection hole facing the
interconnection 14.
[0135] As described above, according to this embodiment, the excess
portion of the conductive paste 13 is removed in the step of
temporarily hardening the paste, in which the paste can be easily
removed, instead of the step after calcination in which the paste
is difficult to remove. For this reason, even if the trench 12
having a large opening diameter is formed to decrease the
resistance of the chip-through plug, the excess portion of the
conductive paste 13 can be removed in a short period of time.
[0136] In addition, in this embodiment, since the conductive paste
13 is buried in the trench 12 after calcination of the ceramic
substrate 11 (after high-temperature heat treatment), a metal paste
having a relatively low resistance, e.g., Ni or Al, which has a
melting point lower than that of a refractory metal such as W can
be used.
[0137] Furthermore, if the thick ceramic substrate 11 is used,
since the substrate can be easily treated, the process required for
the formation of the chip-through plug 13 is facilitated.
[0138] Although the excess portion of the conductive paste 13 is
removed by polishing in this embodiment, this portion may be
removed by etching such as RIE or CDE.
[0139] Note that the excess portion of the conductive paste 13 can
be reliably removed by CMP regardless of the amount of the excess
portion of the conductive paste 13 and its planarization before
polishing. The chip-through plug 13 having a flat upper portion can
therefore be easily formed. If the upper portion is flat, the
interconnection 14 can be easily formed on it.
[0140] (Sixth Embodiment)
[0141] FIGS. 7A to 7G are sectional views showing the steps in a
method of forming a chip-through plug according to the sixth
embodiment of the present invention. In this embodiment, a
chip-through plug is-formed in an Si substrate (Si wafer).
[0142] As shown in FIG. 7A, an interlevel insulating film 22 is
formed on an Si substrate 21 on which a device has already been
formed.
[0143] As shown in FIG. 7B, the interlevel insulating film 22 and
the Si substrate 21 are etched to form a trench 23 having an
opening diameter of 50 .mu.m and a depth of 200 .mu.m.
[0144] As shown in FIG. 7C, after a 1-.mu.m thick silicon nitride
film 24 is formed on the entire surface of the trench 23 to cover
it by a plasma CVD method, a multilayer metal film 25 made up of a
50-nm thick Ti film, a 300-nm thick Ni film, a 50-nm thick Pd film,
and a 4-.mu.m thick Cu film is formed on the silicon nitride film
24. In this case, the Ti, Ni, and Pd films are formed by, for
example, sputtering, whereas the Cu film is formed by, for example,
a plating method.
[0145] As shown in FIG. 7D, the entire surface of the resultant
structure is then coated with a conductive or insulating paste 26,
and the paste 26 having a thickness larger than the depth of the
trench 23 is buried in the trench 23. Thereafter, a temporary
hardening process is performed by volatilizing the solvent of the
paste 26. At this time, a large amount of excess portion of the
paste 26 remains outside the trench 23. In this case, the
conductive paste 26 having a thickness smaller than the depth of
the trench 23 may be buried in the trench 23 as long as the trench
23 can be entirely filled with the paste finally.
[0146] Note that since the aspect ratio of the trench 23 is high, a
paste burying method described in the seventh embodiment is
preferably used to prevent any void from being left in the trench
23.
[0147] As shown in FIG. 7E, the excess portion of the paste 26
outside the trench 23 is removed by CMP. In this case, since the
paste 26 has undergone only the temporary hardening process, the
excess portion of the paste 26 outside the trench 23 can be easily
removed by polishing with a weak force enough to destroy the resin
in the paste 26. As a consequence, as in the fifth embodiment, the
excess portion of the paste 26 can be removed in a very short
period of time as compared with the prior art.
[0148] In addition, the excess portion of the paste 26 can be
easily and selectively removed by adding a solution of the same
solvent as that of the binder contained in the paste 26 or a
solvent solution having a dissolving powder lower than that of the
above solvent to the polishing liquid. Alternatively, instead of
the solution, a weak acid or weak basic solution that dissolves the
binder in the paste 26 may be added.
[0149] In this step, a certain portion of the paste 26 is
preferably left outside the trench 23 for the following reason.
Since the paste 26 shrinks in the next calcination step, if all the
portion of the paste 26 outside the trench 23 is removed, an
unfilled portion is formed in the upper portion of the trench 23
after calcination. If, however, the paste 26 does not shrink much,
no problem arises even if all the portion of the paste 26 outside
the trench 23 is removed.
[0150] After the portion of the multilayer metal film 25 outside
the trench 23 and the silicon nitride film are removed by CMP or
the like, the paste 26 is calcined. The calcined paste 26, the
multilayer metal film 25, and the silicon nitride film 24
constitute a chip-through plug 27. Subsequently, as shown in FIG.
7F, a multilevel interconnection 28 is formed on the Si substrate
21.
[0151] As shown in FIG. 7G, the lower surface of the Si substrate
21 is polished by CMP or the like until the chip-through plug 27
appears, thereby completing the chip-through plug 27 extending
through the Si substrate 21. In this embodiment, as shown in FIG.
7G, the multilayer metal film 25 is etched when the lower surface
of the substrate is polished. Even if, however, this process is
performed such that the multilayer metal film 25 is left in the
bottom portion of the chip-through plug 27, no problem arises. The
subsequent steps are the same as those for a general multichip
module. For example, the step of connecting a plurality of Si
substrates 21 to each other through chip-through plugs 27
continues.
[0152] As described above, according to this embodiment, the excess
portion of the paste 26 is removed in the step of temporarily
hardening the paste, in which the paste can be easily removed,
instead of the step after calcination in which the paste is
difficult to remove. As in the first embodiment, therefore, the
low-resistance chip-through plug 27 can be formed without taking
much time. In addition, this embodiment can be modified in the same
manner as the fifth embodiment. For example, the excess portion of
the paste 26 may be removed by etching instead of polishing.
[0153] (Seventh Embodiment)
[0154] FIGS. 8A to 8D are sectional views showing the steps in a
method of forming a chip-through plug according to the seventh
embodiment of the present invention.
[0155] As shown in FIG. 8A, a trench 32 of a high aspect ratio is
formed in an Si or ceramic substrate 31. For example, the trench 32
has an opening diameter of 100 .mu.m and a depth of 150 .mu.m.
[0156] As shown in FIG. 8B, the substrate 31 is coated with an Ni
paste 33, and the trench 32 is filled with the Ni paste 33 to some
level from the opening surface of the trench 32. In this stage, a
void (unfilled region) is present on the bottom surface side of the
trench 32.
[0157] When an Si substrate is used as the substrate 31, an
insulating film such as a silicon nitride film 24 for providing
insulation for the Si substrate is formed in advance on the surface
of the trench 32, as in the sixth embodiment. In addition, as in
the sixth embodiment, the substrate may be coated with an
insulating paste through a conductive film such as a multilayer
metal film 25 instead of the Ni paste 33.
[0158] As shown in FIG. 8C, the Ni paste 33 is pressurized with
N.sub.2 gas 34 of a high pressure, e.g., 2 kgf/cm.sup.2 to fill the
void in the trench 32 with the Ni paste 33, thereby entirely
filling the trench 32 with the Ni paste 33, as shown in FIG.
8D.
[0159] The subsequent steps are the same as those in the fifth and
sixth embodiments. For example, a temporary hardening process is
performed at a temperature of 100 to 150.degree. C. to remove the
portion of the Ni paste 33 outside the trench 32. The Ni paste 33
is then calcined at a temperature of 600.degree. C. The lower
surface of the substrate 31 is polished until this calcined Ni
paste 33 appears, thereby completing a chip having the Ni paste 33
penetrating the Si substrate 33.
[0160] As described above, according to this embodiment, after the
Ni paste 33 is buried in the trench 32 to a certain extent, the
void in the trench 32 is filled with the Ni paste 33 by
pressurizing the portion of the Ni paste 33 outside the trench 32.
With this process, even if the depth (aspect ratio) of the trench
32 increases, the trench 32 can be easily filled with the Ni paste
33.
[0161] According to this embodiment, even if, therefore, the depth
of the trench 32 increases, the Ni paste 33 without any void can be
formed.
[0162] In this embodiment, after the substrate is coated with the
Ni paste 33, the Ni paste 33 is pressurized with a gas. However,
this paste may be mechanically pressurized to fill the void in the
trench 32 with the Ni paste 33. Alternatively, after the substrate
is coated with the Ni paste 33 under a reduced pressure, the
pressure may be restored to atmospheric pressure, thereby filling
the void in the trench 32 with the Ni paste 33.
[0163] The present invention is not limited to the above
embodiments. For example, in each embodiment described above, the
paste according to the-present invention is applied to a
chip-through plug. However, this paste can be applied to other
members such as damascene interconnections. Various changes and
modifications of the embodiments can be made without departing from
the spirit and scope of the invention.
[0164] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *